Q1 2010 / If CO2 incubation is your game – Protect your investment

If you are a researcher in any of the life sciences, the chances are good that you have one or more incubators chock full of samples that represent years of work and may well represent the entire value of the company – especially if you are a startup operation. 

These incubators need to be constantly supplied with carbon dioxide. Lose the CO2 atmosphere and you could lose your samples along with much of your research.

Many researchers are aware of this danger, but choose to ignore it because “they have never had a problem.” Considering the investment costs associated with the stored samples, this is not a prudent way to operate. Your gas supply system should be designed to ensure that you always have a gas supply, or at least that you are notified if your gas supply gets low. It has been our experience that those that have a casual attitude toward their carbon dioxide supply system pay the price sooner or later.

Understanding carbon dioxide

Carbon dioxide is not like most gases. Because of its unusual phase diagram it exhibits some strange behaviors at times. As dry ice, for example, it is a solid that does not melt but sublimes – going from solid to vapor as it warms without first forming a liquid state.

In a cylinder it is a liquefied gas under its own vapor pressure of 830 psig @70° F. However, raise the temperature to 88° F (its critical temperature) and the contents of the cylinder will all turn to gas at approximately 1,057 psig with no liquid present in the cylinder.

At normal room temperature, when there are both liquid and gas phases present in the cylinder, the pressure remains at about 830 psig – as long as the gas removal rate is less than five pounds per hour. Once the contents of the cylinder reaches 9.5 pounds no liquid remains and the pressure declines continuously until the cylinder is empty. At this changeover point a standard 50-pound cylinder has about 93-cubic-feet of CO2. This means the only way to know the true contents of a CO2 cylinder is by weight.

Now consider a researcher operating with a single cylinder connected to an incubator. He is relying on the inlet pressure gauge of the pressure regulator to tell him when he needs to change cylinders. He looks at the gauge at 5 p.m. on Friday as he heads home for the weekend.

 Shortly after he walks out the door, the pressure gauge reading falls to 820 psig. The question becomes, “Is there sufficient gas to supply his incubator until he returns on Monday, or will the cylinder run dry and the flow of carbon dioxide cease?” The situation becomes even riskier if it happens to be a holiday weekend like Thanksgiving and that 93-cubic-feet of gas must last 4.5 days.

General requirements

Although there are numerous solutions to ensure that gas supply remains constant take a look at these general types of equipment I believe help ensure that the required protection is adequate.

First, a changeover manifold with at least one cylinder on each side provides the best protection if it has an alarm system that tells you when the “in service” side has switched to the “standby” side. This warning system can also be connected to an auto-dialer that can notify your supplier that you need a refill cylinder or cylinders. Depending on your other operational requirements you may opt for an electronic changeover like the Ultra-Logic and the Auto-Logic or a semi-automatic unit like the flip-knob 914 – Figures 1,2 & 3.

Second, an electronic cylinder scale (Figure 4, below) provides notification that the cylinder needs to be replaced. Setting an alarm at a cylinder net weight ensures that there is sufficient gas to last until a replacement cylinder is on hand. This system can be connected to an auto-dialer or other warning device as well.

Third, a dual-protocol station with two cylinders, one in service and the other in reserve – sort of a manual changeover system. This installation can be fitted with an alarm set at 500 psig to warn that the “in service” cylinder is almost empty (Figure 5). However, if someone is not present to open the other cylinder when the alarm goes off the researcher will still run out of gas and the samples will be jeopardized.

Lastly, install a cylinder scale to monitor the contents. Be diligent and check the scale regularly so that the cylinder is changed when the contents become low.

Summary

The price range difference between the optimal solution and an inadequate one is about $3,000 to $4,000. Considering what is at stake if the firm lost all its samples by running out of CO2, isn’t the investment in the right equipment worth the extra cost? Most researchers would spend that money in a heartbeat if someone told them that they were going to lose everything, but that everything could be saved if they paid their new “hero” $5,000.